The present invention relates to heat-insulating stock material and methods for producing the stock material and containers. More particularly, the present invention is directed to the formation of insulating stock material formed by selectively adhering a polymer film to a paperboard substrate and forming containers from the insulating stock material.
Several types of heat-insulating containers have been used commercially to pack hot liquids. A polystyrene foam heat-insulating container is one example. It is prepared by casting unfoamed polystyrene into a mold, heating the resin under pressure to foam it, and removing the foamed resin from the mold. Alternatively, a foamed styrene sheet may be shaped into a container. An initial drawback of these types of containers is that their insulating characteristics are so efficient that the consumer can be lulled into a false sense of security because the outside of the cup is not hot while the temperature of the contents remain scalding. The container thus produced has outstanding heat-insulating properties but, on the other hand, it needs reconsideration from the viewpoint of saving petroleum resources or increasing the efficiency of incinerating waste containers. As a further problem, a slow, inefficient and high waste printing process is required to print on the outer surfaces of polystyrene foam heat-insulating containers since printing can only be effected after individual cups have been shaped. Further, the tapered surface of the container contributes to print blur at positions near the top and bottom of the container unless specialized and expensive printing technology is employed. As a further disadvantage, the outer surface of the foamed styrene heat-insulating container is often not sufficiently smooth to accept high resolution screen printing further affecting printability. Thus, the polystyrene foam containers suffer the disadvantage of low printability.
The conventional paper heat-insulating container can not be manufactured at low cost, and one reason is the complexity of the manufacturing process. One example is a container wherein the side wall of the body member is surrounded by a corrugated heat-insulating jacket. The process of manufacturing such containers involves additional steps of forming the corrugated jacket and bonding it to the outer surface of the side wall of the body member. One defect of this type of container is that letters, figures or other symbols are printed on the corrugated surface and the resulting deformed letters or patterns do not have aesthetic appeal to consumers. Another defect is that the jacket is bonded to the side wall of the body member in such a manner that only the valley ridges contact the side wall, and the bond between the jacket and the side wall is so weak that the two can easily separate. Often times, corrugated containers are not suitable for stacking and thus require large storage space.
U.S. Pat. No. 4,435,344 issued to Iioka teaches a heat-insulating paper container consisting of a body member and a bottom panel member, characterized in that at least one surface of the body member is coated or laminated with a foamed heat-insulating layer of a thermoplastic synthetic resin film whereas the other surface of the body member is coated or laminated with a thermoplastic synthetic resin film, a foamed heat-insulating layer of thermoplastic synthetic resin film or an aluminum foil. When manufacturing such a container, the water in the paper is vaporized upon heating, causing the thermoplastic synthetic resin film on the surface to foam. The container under consideration has the advantage that it exhibits fairly good heat-insulating properties and that it can be manufactured at low cost by a simple process. However, the thermoplastic synthetic resin film will not foam adequately if the water content in the paper is low. While high water content is advantageous for the purpose of film foaming, the mechanical strength of the container may deteriorate. Moreover, even if successful foaming is done, the thickness of the foam layer is uniform and cannot be controlled from one portion of the container to another. Further, the foam layer reaches an expansion limit regardless of the moisture content of the base layer.
In an effort to overcome the aforementioned shortcomings, U.S. Pat. No. 5,490,631 issued to Iioka discloses a heat-insulating paper container including a body wherein part of the outer surface of the body members provided with a printing of an organic solvent based ink. The body portion is subsequently coated with a thermoplastic synthetic resin film which when heated forms a thick foamed heat-insulating layer in the printed area of the outer surface whereas a less thick foamed heat-insulating layer is formed in the non-printed areas. Further, there are portions of the outer surface which remain unfoamed. In manufacturing a container in this manner, the printing is carried out on the paperboard layer and consequently viewing of the printed matter by the consumer is obstructed by the foamed insulating layer. Moreover, because the foamed layer overlying the printed areas are thicker than the remaining portions of the foamed layers, these areas will be even more obstructed. Consequently, this container suffers from similar drawbacks as those containers discussed hereinabove.
Another type of paper heat-insulating container has a xe2x80x9cdualxe2x80x9d structure wherein an inner cup is given a different taper than an outer cup to form a heat-insulating air layer. The two cups are made integral by curling their respective upper portions into a rim. The side wall of the outer cup is flat and has high printability, however, the two cups may easily separate. Another disadvantage is that the dual structure increases the manufacturing cost and thus the unit cost of the container. Moreover, the dual cup construction increases the stacking height of the cups and consequently increases packaging and shipping costs.
Accordingly, there is a need for insulated stock material and containers wherein the stock material can be manufactured in an economical manner such that the resultant containers formed from the insulating stock material provide the requisite insulating properties while readily receiving printed matter on the outer surface of the material.
A primary object of the present invention is to overcome the aforementioned shortcomings associated with the containers discussed hereinabove.
A further object of the present invention is to provide a heat insulating stock material which may be economically manufactured and readily formed into containers for receiving a hot liquid.
Yet another object of the present invention is to provide a decorative heat-insulating container and stock material for forming the same wherein the outer surface of the insulating material readily receives printed indicia.
Yet another object of the present invention is to provide a heat insulating container including a plurality of pockets which readily expand in response to a hot liquid being placed in the container thereby forming an insulating barrier between the hot liquid and the consumer.
Still another object of the present invention is to provide methods of forming the heat insulating stock material in a manner which adds little to the overall cost associated with the formation of such containers.
A still further object of the present invention is to provide a heat insulating container and stock material for forming the same which includes not only enhanced insulating characteristics but which provides for little increase in the stacking height of the containers.
These as well as additional advantages of the present invention are achieved by forming an insulating container comprising a container body having a side wall and a bottom wall with the one side wall including a base layer and an insulating layer on at least a portion of the base layer, preferably on an inside surface of the side wall. The insulating layer being selectively adhered to at least a portion of the base layer such that the selective adhering of the insulating layer to the base layer creates air pockets between the insulating layer and the base layer with the air pockets being expandable in response to contact with a heated liquid. Such a container is formed from an insulating stock material comprising a paperboard base layer and an insulating layer overlying at least a portion of at least of one surface of the base layer with the insulating layer being selectively adhered to the surface of the base layer forming enclosed regions between the base layer and the insulating layer. In order to ensure the formation of pronounced air pockets between the insulating layer and the base layer, the paperboard base layer may be debossed, creating debossed regions with the insulating layer being adhered over the openings of the debossed regions.
These as well as additional advantages of the present invention will become apparent from the following detailed description when read in light of the several figures.